The broad objectives of the proposed research are: 1. To obtain structural information regarding the sununit composition, ligand binding sites and conformational equilibria of an acetylcholine receptor both in purified form and its membrane associated state. 2. To develop a new and general procedure for non-destructive affinity labelling of an acetylcholine receptor which can be used to introduce fluorescent, nmr, e.p.r. or other probe moieties into proteins. 3. To conduct equilibrium binding studies on the two classes of ligand binding sites in acetylcholine receptor from Torpedo californica in order to further elucidate the properties of the ligand binding sites. 4. To obtain the kinetic parameters of binding for acetylcholine and other cholinergic ligands to acetylcholine receptor molecules in order to relate such parameters to electrophysiological time constants in vivo. 5. To reconstitute isolated acetylcholine receptors with phospholipids so that it may be possible to determine whether a single macromolecule performs both the function of acetylcholine binding and of ionophore in post-synaptic transmission. 6. To assimilate all structural, conformational, kinetic and equilibrium binding studies to produce a model at the molecular level sufficient to explain post-synaptic transmission.